A heme containing fragment of cytochrome c consisting of amino acid residues 1 through 38 (1-38H) was prepared by tryptic digestion of the native molecule. Apocytochrome c (1-104) has also been prepared by removal of the heme moiety through standard chemical techniques. On mixing these two fragments a noncovalently linked 1:1 complex is formed, and the spectral properties and biological activity of this complex are essentially identical to native cytochrome c. The redundant residues of this native-like complex were removed by tryptic digestion of the material in its reduced form (Fe ion 2). Subsequent separation and identification of the remaining complementing fragments revealed that two distinct complexes are formed from the initial mixture of (1-38H) and apoprotein. Thus one complex consists of residues (1-25H) from the original (1-38H) fragment and residues (23-104) from the apoprotein, while a second complex utilizes the entire (1-38H) fragment and residues (56-104) from the apoprotein. In addition, we have shown that these native-like species may be regenerated by mixing the appropriate non-overlapping fragments. Biologically active complexes have been prepared from mixtures of (1-25H) plus (23-104) and (1-38H) plus (56-104) as well as (1-38H) plus (39-104).